Security EventID 676

Currently the eventlogs on our Win2k SP4 server has a number of security logs in the middle of the night and they are referenceing eventID 676 with the info below.

Authentication Ticket Request Failed:
       User Name:      barbara
       Supplied Realm Name:      FNBHAYS.COM
       Service Name:      krbtgt/FNBHAYS.COM
       Ticket Options:      0x40810010
       Failure Code:      0x12
       Client Address:

The usernames vary and sometimes are blank. Logins are disable from 7pm to 7am and there is nobody present on-site etc.

Any insight would be appreciated on what may be happening
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Sometimes a logon fails not because of a bad password but because the user mistyped the username or tried to guess someone else's username.
If a logon fails because of an invalid username, Windows 2000 logs event ID 676 (authentication ticket request failed) with Failure Code 6. This event is another important logon auditing advance because in NT you can't distinguish logons that failed because of a bad password from logons that failed because of a bad username. Windows 2000 uses event ID 676 with other failure codes to identify several other types of failed-logon situations.

Failure Code 12 indicates the logon failed because of time-of-day or workstation restrictions. Failure Code 18 signifies that the account was locked out because of failed logons, disabled by the administrator, or expired.
Failure Code 23 means the user's password had expired.
Failure Code 37 occurs when a workstation's clock was too far out of synchronization with the DC's clock.

See Audit Account Logon Events for more details.

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nextech01Author Commented:
I would agree that  it is a failed user logon but when this is happening there is no one on-site because it happens in the middle of the night a lot of times, I have included another bit from one of the logged events;

Service Ticket Request Failed:
       User Name:      FNBPDC$
       User Domain:      FNBHAYS.COM
       Service Name:      krbtgt/FNBHAYS.COM
       Ticket Options:      0x2
       Failure Code:      0x20
       Client Address:

In this case the server name is FNBHAYS and happened at 5:17am and what is confusing is the username FNBPDC$ which may be a service but it is occuring on this server named FNBPDC.

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